How to draw a nonfunction line plot with Plotly?

Question

I'm using plotly in R, though I don't think it should matter. Basically, I want to draw a line plot of a set of points that don't correspond to a function (in the mathematical sense). See the below code for a simple example, I think it's fairly obvious what the problem is. I want the second plot to simply look like the first one inverted across the x/y axes.

To clarify, the example below could be solved be using the inverse function (square root), but I'm looking for a generic solution that doesn't rely on having an explicitly invertible function.

library(plotly)
library(magrittr)

x <- seq(from=-2, to=2, length.out = 200)
y <- x^2

p1 <- plot_ly() %>%
  add_lines(x=x, y=y)

p2 <- plot_ly() %>%
  add_lines(x=y, y=x)

vestland · Accepted Answer · 2021-09-03 07:09:46Z

1

I really think this would depend completely on the specifics of your dataset. In your data sample, you've got a unique x-value for each y. The reason your second figure fails (in the sense that you're not getting a smooth continuous line), is that you no longer have a unique value on your x-axis for each value on your y-axis. To get the visual result you seem to be looking for with this particular dataset, you could separate positive and negative numbers for your y axis and apply two traces:

Complete code:

library(plotly)
library(magrittr)


x <- seq(from=-2, to=2, length.out = 200)
y <- x^2

df1 = data.frame(x1=x,
                y1=y
                )

df2 <- filter(df1, x1 <= 0)
df3 <- filter(df1, x1  > 0)


p1 <- plot_ly() %>%
  add_lines(data=df2, x=~y1 , y=~x1, line = list(color = '#636EFA', width = 1.5))

p1 <- p1 %>% add_lines(data=df3, x=~y1 , y=~x1, line = list(color = '#636EFA', width = 1.5))

p1

edited Sep 3, 2021 at 7:09

answered Apr 27, 2020 at 10:10

vestland

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1 Comment

Ben Over a year ago

This is exactly what I ended up doing for the case I was trying to work with, though my concern is that it doesn't generalize very cleanly. For an arbitrary set of data you'd need to split it along some y-value, identify each different branch, and separate them. It's remarkable to me that there doesn't seem to be an easier way within plotly, especially given the ease of--for example--making a histogram on the y-axis instead of the x.

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